Chair iron

ABSTRACT

The preferred embodiment of the chair iron includes a seat platform pivotally mounted to a frame which in turn is supportable by a chair base. A torsion rod is mounted on the frame with one end fixed and one end free to rotate. A second torsion rod is similarly mounted on the platform, parallel to the first. A pair of levers are slidably mounted on the rods and are maintained in alignment by a bracket assembly. This assembly also includes a cam and pin arrangement whereby a pretension force can be applied to the levers and thereby to the torsion rods.

D United States Patent 1151 3,659,819 Wolters 1 May 2, 1972 1 CHAIR IRON 3,552,796 1/1971 Williams ..297/304 [72] Inventor: Richard H. Walters, East Grand Rapids, FOREIGN PATENTS 0 APPLICA'HONS Mich.

1,222,689 8/l966 Germany ..248/373 [73] Assignee: Steelease lnc., Grand Rapids, Mich. [221 Filed: June a 1970 Primary Examiner-J. Franklin Foss App]. No.: 43,995

[52] [1.8. CI ..248/373, 297/304 [51] Int. Cl ..A47c 3/00 [58] Field ofSeru-ch ..248/373,399, 387,372;

[56] Reierences Clted UNITED STATES PATENTS 3,027,191 3/1962 Lie ..297/306 3,423,060 1/1969 Fulling et a]. ...248/399 3,240,528 3/1966 Ciuftmi ..297/303 At!0rneyPrice. Heneveld, Huizenga & Cooper ABSTRACT The preferred embodiment of the chair iron includes a seat platform pivotally mounted to a frame which in turn is supportable by a chair base. A torsion rod is mounted on the frame with one end fixed and one end free to rotate. A second torsion rod is similarly mounted on the platform, parallel to the first. A pair of levers are slidably mounted on the rods and are maintained in alignment by a bracket assembly. This assembly also includes a cam and pin arrangement whereby a pretension force can be applied to the levers and thereby to the torsion rods.

38 Claims, 9 Drawing Figures Patented May 2, 1972 4 Sheets-Sheet 1 FIGJ 6O 72 73 TI 64 TO FIG.2

Patented May 2, 1972 3,659,819

4 Sheets-Sheet a INVENTOR- IP/L'AIAQPD A. M4755 BYQW 1 Patented May 2, 1972 4 Sheets-Sheet :5

n a B/ m m \m 7 lI/II b 1 0 1 4 I b /4 3 O/ m v a 7\ 3 FIG. 7

FIG. 5

sea.

I 1 1 1 1/ II 1111] 17 II 11 11 II FIG. 6

WTOKd/EKS Plhntod May 2, 1972 4 Shun-Shut 4 .I. I l I I I I I I I- I x Y I I U REPONSE OF DIR MIMI FIG. 8

TORQUI REQUIRED TO TILT CHAIR RESPON5E OF PREFERD EMBODIMENT HAS MEANQ FIG. 9

INVENTOR 2/41/1900 uazns'es BACKGROUND A chair iron comprises a stationary member mounted on a chair base, and a seat member which tilts with respect to the stationary member. A bias member, generally a coil spring or a torsion bar, acts between the seat member and the stationary member, or the base, in order to control the rate at which this tilting action can take place. Almost all chair irons include a means for setting a pretension on the bias member. This pretension must be overcome by a positive force before the chair will begin to tilt. Once the chair beings to tilt, the rate at which it can be tilted, i.e., its tilt rate, is a function of the rate of change curve for the bias member, be it a torsion rod or coil spring. The rate ofchange curve for a torsion rod would be the torque required to twist the rod plotted against the degrees of twist imparted to the rod. For a coil spring, this curve would be the force required to compress or extend the spring plotted against the extent compression or extension of the spring.

FIG. 8 shows a graph on which the torque which a person would apply to a chair by tilting it rearwardly is plotted against the response of the bias member, i.e. the degrees of twist in a torsion rod or the extent of compression or extension of a coil spring. The curve labeled with the number 1 is a hypothetical curve for a prior art bias member which, for purposes of discussion, shall be assumed to be a torsion rod.

As is well known in the art, one can set the pretension of the torsion rod by imparting to it an initial twist, i.e., without tilting the chair, a heavier person usually desires a greater pretension than a lighter one. If a person desired a pretension A, he would impart a twist of U to the rod. (If a coil spring were used, he would compress or extend the spring U inches.) Thus, in order to tilt the chair at all, a person would have to first apply a torque A thereto.

Tilt chairs are usually constructed so that they can be tilted through about 18". With respect to our hypothetical prior art torsion rod, one of its ends would be twisted from U to V". (In most conventional constructions, if not all, the difference between U and V would also be 18.) The tilt rate of the chair would be a function of the slope of curve number 1 between U and V.

If one desired a greater pretension, for example a pretension B, he would impart an initial twist W to the torsion rod. Tilting the chair through l8 would further twist the rod to Y". The tilt rate of the chair with a pretension of B would be a function of the slope of curve 1 between W and Y.

If the pretension setting of our hypothetical prior art torsion rod is B, the tilt rate for the chair is less than it is for a pretension setting of A. In other words, at B, a given increase in torque; over and above the pretension level, will cause the chair to tilt less rapidly than would the same increment of torque above pretension A.

If the bias member had a linear rate of change curve, then the tilt rate for the chair would always be the same regardless of the pretension setting. Of course, a heavier person might well appreciate a steeper tilt rate than a lighter person. Thus, one might try to select an ideal spring or rod in a chair iron suitable for all people. A rate of change curve for such a chair iron might be as illustrated by curve 2 in FIG. 8. Although an ideal spring might be possible, it would not only be difficult to find such, but also such a spring might not in fact satisfy all people. Individual taste would deviate greatly from the norm. Thus, the point is that no matter what the rate of change curve for the bias member looks like, no chair iron currently available offers a means whereby one can choose not only a desired pretension level independent of tilt rate, but also a desired tilt rate independent of pretension. Once they choose a given pretension, they must be satisfied with a given tilt rate. Put in another way, no iron is currently available in which the rate of change curve for the bias member can be varied.

Furthermore, most chair irons currently available are large, bulky and expensive to manufacture. The torsion bar chair iron in particular must generally be so long that it becomes unsightly.

SUMMARY The present invention is a chair iron in which the above disadvantages are met by providing a means whereby both tilt rate and pretension can be selected independently of one another. The rate of change curve for the bias member can be varied.

Another aspect of this invention makes possible the elimination of bulky torsion bar chair controls or irons by providing a control in which one torsion bar is fixed against rotation with respect to the frame, a second bar is fixed against rotation with respect to the platform and the two bars are interconnected by a unique interconnecting means whereby rotation of one of the rods generates rotation in the other. In a preferred aspect of the invention, the interconnecting means also includes a means for pretensioning the torsion means. In effect, the two bars cooperate together as though they were one bar. Thus, if the chair or a portion of the chair is tilted through [8", each rod will be twisted through only approximately half that number of degrees. Accordingly. each rod can be approximately one-half the length of a single rod and can be placed in a much smaller and more compact housing, and this result is achieved without sacrificing an ability to pretension the torsion means.

The interconnecting means comprises a first lever extending inwardly from one bar and a second lever extending inwardly from the other with bracket means holding the ends of the levers in juxtaposition. This enables one to mount a movable member on the bracket and operably connect it to the levers to impart a force to the levers and thereby pretension the torsion bars.

Thus, with this invention a person cannot only choose a desired pretension for his chair, but he also can choose any given rate at which the chair can be tilted, regardless of his choice of pretension. Additionally, this invention provides a chair iron which is compact and which can be economically manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a bottom view of the chair iron;

FIG. 2 is a cross section taken along plane Il-ll of FIG. 1;

FIG. 3 is a slightly elevated perspective view of the control mechanism;

FIG. 4 is a perspective view of the control mechanism from the bottom;

FIG. 5 is a cross-sectional view of the chair iron taken along plane Il-Il of FIG. I, only with the seat platform being tilted with respect to the frame,

FIG. 6 is a cross-sectional view taken along plane Vl-Vl of FIG. 1;

FIG. 7 is a cross-sectional view taken along plane VII-VII of FIG. 1',

FIG. 8 is a graph showing hypothetical curves for prior art bias members with the torque required to tilt a chair being plotted against the response of the bias member;

FIG. 9 similarly shows a number of hypothetical curves for the preferred embodiment bias means with the torque required to tilt a chair being plotted against the response of the bias means.

PREFERRED EMBODIMENT Referring to FIG. I, the preferred embodiment comprises generally a frame 10, a seat platform 30 being pivotally mounted thereto, a pair of levers 51 and 54 on torsion rods 2l and 41, respectively, a bracket assembly 60 holding these levers in juxtaposition, and a cam member 70 mounted on bracket 60.

Frame 10 is preferably formed of metal, either by bending or casting. It is generally pan-shaped in that it has a right side lla, lelt side llb, front 12 and a top 13. Instead of having a back side, it has a sloped surface or stop 14 which acts to limit the extent to which a chair mounted on this iron can be tilted rearwardly.

Mounted on the underside of top 13 and sloped stop 14 is a spindle mounting 15 (FIG. 1). This could hold a rigid spindle or the like, but the particular mounting of frame 10 to the chair base is not particularly important. For example, frame 10 could itself rotate upon a spindle rather than being rigidly secured thereto.

Rigidly secured to the inside of left side 11b is a torsion rod mounting plate 16 (FIG. 1). It is secured thereto by means of rivet 17. It includes a square hold 18 extending therethrough into which a square torsion rod 21 can be fitted (FIG. 7). Side 11a has a slightly elliptical hole 19 (FIG. 6). A round bushing 22 having a square hole therethrough is slipped over the other end of square torsion rod 21, slid into elliptical hole 19, and tightened in place by means of a set screw or the like. In this fashion, torsion rod 21 is mounted between the ends of frame 10 with one end being freely rotatable, as at side 11a, and the other end being fixed against rotation, as at side 11b.

Seat platfonn 30 is also preferably made of metal and is generally pan-shaped. It includes right side 31a, left side 31b, back 32 and top 33 (FIG. 1). There is no front side and there is no need for a stopping surface such as sloped stop 14 of frame 10.

Platform 30 also includes a pair of mounting arms 34a and 34b (FIG. l). Each juts inwardly slightly from its respective side 31a or 31b and then extends in a parallel fashion to sides 31a and 31b. Right mounting arm 34a includes a hole through which a mounting bolt 450 can be fitted. Similarly, a mounting bolt 45b can be fitted through a hole in mounting arm 34b. Mounting bolts 45a and 45!) are then threaded into threaded holes (not visible) near the inwardly extending ends of sides 11a and 11b respectively. In this fashion, platform 30 is pivotally secured to frame 10.

Rigidly secured to left side 31b of platform 30 is a rod mounting plate 35. It is held against side 31b by means of rivet 36. It also includes a square hole 37 extending therethrough into which a square torsion rod 41 can be fitted (FIG. 7). Side 310 of frame 30 includes an elliptical hole 38 (FIG. 6). A round bushing 42 having a square hole therethrough is fitted over square torsion rod 41. It is then fitted into elliptical hole 38 and tightened in place by means ofa set screw or the like. In this fashion, torsion rod 41 is mounted between the ends of platform 30 with one end being fixed against rotation and the other being free to rotate. It will be noted that the freely rotatable ends of both torsion rods 21 and 41 are located at right sides 11a and 31a respectively and the fixed ends of both torsion rods 21 and 41 are located at the left sides 1 lb and 31b respectively.

Finally, connected to either side 31a and 31b of platform 30 are a pair of seat mounting arms 39a and 39b. These include mounting holes 40 whereby a seat can be secured thereto.

Lever 51 is preferably formed of metal and has converging end portions so as to be shaped somewhat like an elongated V. It has a square hole 52 near its widest end and a projection 53 extending upwardly from its opposite end (FIG. 3). It is slidably mounted on torsion bar 21 which extends through square hole 52. Because the torsion rod 21 is square and hole 52 is square, lever 51 will not rotate with respect to torsion rod 21. It is slidable along at least a portion of the length thereof.

Lever 54 is identical in configuration, having square hole 55 and projection 56 (FIG. 3). It is mounted on torsion rod 41 in the same manner in which lever 51 is mounted on torsion rod 21.

Levers 51 and 54 both extend inwardly towards each other (FIGS. 2, 3 and 4). They are sufficiently short in length that they will not touch even when arranged in direct juxtaposition. They are maintained in juxtaposition by means of bracket 60.

Bracket 60 is a channel-shaped member having side walls 61 and a bottom 62 (FIGS. 3 and 4). There is an aperture 63 in the center of bottom 62 through which a pin 65 extends (FIG. 4).

Pin 65 is shaped generally like a T having a bar or cross 66 at its top (FIG. 3) and a hook 69 at its lower foot or end (FIG. 4). There is a slight notch 67 under the right side of bar or cross 66 and a similar notch 68 under the left side of cross 66 (FIG. 3). These notches conform to projections 53 and 56 on levers 51 and 54. Pin 65 is movable within bracket 60 and in aperture 63. Integrally secured to the outside of bottom 62 is a back stop 64 (FIG. 4). It is located adjacent aperture 63 such that pin 65 may be pushed against it.

Secured to the underside or exposed side of bottom 62 is a cam assembly 70 (FIG. 4). It includes a cam disc 71 which is rotatably mounted to bottom 62 by means of rivet 75. Cam disc 71 is located closely adjacent aperture 63. It includes an arcuate inclined ridge or cam surface 72 running around slightly more than half of the perimeter of the cam disc. A stop 73 extends upwardly from the top or uppermost end of inclined ridge 72. A lever 74 is integrally secured to disc 71 and extends outwardly therefrom.

Levers 51 and 54 are maintained in direct juxtaposition by being channeled in bracket 60 (FIGS. 1, 3 and 4). Each lever 51 and 54 is maintained in place by the channel walls 61 of bracket 60. Each end of bottom 62 comprises a fulcrum which engages a lever 51 or 54. Bracket 60 is held in place by means of pin 65, with the ends of bottom 62 engaging levers 51 and 54. Cross member 66 extends over the end of lever 51 on one side and over the end of lever 54 on the other side. Projection 53 on lever 51 fits snugly into notch 67 and projection 56 on lever 54 fits snugly into notch 68 (FIG. 3).

Pin 65 then extends downwardly between the ends of levers 51 and 54 and out through aperture 63 in bottom 62 (FIG. 4). Hook portion 69 extends out over the inclined ridge 72 of cam 70. The length of pin 65 is such that when hook 69 is engaging inclined ridge 72 at its lowest point, bracket 60 is maintained in place on levers 51 and 54 without any force being exerted on the ends of levers 51 and 54.

OPERATION The operational heart of the chair iron is the adjusting assembly comprised of levers 51 and 54, bracket 60 and cam 70. When cam means 70 is rotated to the position where hook 69 of pin 65 engages the lowest portion of inclined ridge or cam surface 72, there is no force on levers 51 and 54 and one can slide the entire adjustment assembly along torsion rods 21 and 41. In this manner, one varies the effective length of the torsion rods by varying the distance between the levers 51 and 54 from the fixed ends of torsion rods 21 and 41.

Upon reaching a given desired position along the length of torsion rods 21 and 41, one can tighten in place the assembly comprised of levers 51 and 54, bracket 60 and cam 70 merely by rotating cam 70 via lever 74. This moves hook 69 upwardly on inclined ridge 72 thereby tightening down cross 66 on projections 53 and 56. In effect, as pin 65 is pulled downwardly by means of cam 70, levers 51 and 54 are pivoted about their fulcrums 0n bracket 60, i.e., the ends of channel base 62. Actually. the motion is not entirely pivoting in that some sliding between the levers S1 and 54 and base 62 takes place.

It will be noted that as levers 51 and 54 extend inwardly, they must slope upwardly from their point of contact with base 62 in order that a fulcrum effect can be achieved and the levers 51 and 54 thereby rotated with respect to bracket 60 (FIG. 2). If levers 51 and 54 contacted base 62 at their ends, or over a substantial distance, then there could be no effective rotation of levers 51 and 54 by means of pin 65 and there could be no corresponding twisting of torsion rods 21 and 4 1.

The farther that cam 70 is rotated in a counterclockwise direction as viewed in FIG. 1 or FIG. 4, the farther pin 65 is pulled downwardly through aperture 63 and the more twist is imparted to torsion rods 21 and 41. By use of cam 70 in this fashion, a twist can be imparted to torsion rods 21 and 41 without even tilting seat platform 30. Thus, this action effects a pretension setting for the chair iron.

When one sits in and tips rearwardly a chair mounted on platform 30, platform 30 tilts rearwardly as shown in FIG. 5. Bushings 22 and 42 are free to slide slightly in elliptical holes 19 and 38 in order to minimize stress in the adjustment assembly caused by slight changes in distance between holes 19 and 38 during such rotation.

Because the ends of levers 51 and 54 remain fixed with respect to each other, torsion rod 21 is in effect operably connected to platform 30 through the adjustment assembly and torsion rod 41 is in effect operably connected to frame through the adjustment assembly. Thus, the tilting of platform 30 exerts a force on the end of lever 51 through lever 54, bracket 60 and pin 65. Since lever 51 is fixed against rotation with respect to torsion rod 21 and since one end of torsion rod 21 is fixed, torsion rod 21 is twisted by the tilting of platform 30. Similarly, frame 10 exerts a force on the end of lever 54 through lever 51, bracket 60 and pin 65. Since lever 54 is fixed against rotation with respect to torsion rod 41 and since one end of torsion rod 41 is fixed against rotation, torsion rod 41 will also be twisted by the tilting of platform 30.

The combined twisting of torsion rods 21 and 41 acts to resist the tilting motion of platform 30 and bias platform 30 and frame 10 to a normal position with respect to each other. Thus, platform 30 and frame 10 are biased towards the normal position shown in cross section in FIG. 2 with arms 39a and 39b resting against top surface 13 of frame 10. The rearward tilting of platform 30 is limited by seat mountings 39a and 39b contacting slop stop surface 14 of frame 10 (FIG. 5

The rate of change curve for rods 41 and 42 can be varied and will be determined by the position of the adjustment assembly, i.e., levers 51 and 54, channel 60 and cam 70, along the length of rods 21 and 41. This is illustrated by hypothetical curves in FIG. 9 which shows the torque required to tilt a chair rewardly against the response of the preferred embodiment bias means, i.e., the combined degrees of twist in the dual torsion rods. 1f the adjustment assembly is positioned closer to the fixed ends of rods 21 and 41, then the rate of change curve will be quite steep and might be exemplified by curve number 3 in FIG. 9. On the other hand, if adjustment assembly 50 is positioned farther from the fixed ends of rods 21 and 41, then one will obviously have a more gradual rate of change curve as might be exemplified by curve number 8 in FIG. 9.

Between these positions, there would be an infinite number of rate of change curves of which those designated by reference numerals 4, 5, 6 and 7 are exemplary. If a person were to desire a low pretension as indicated at A of FIG. 9, he could not only choose such a pretension level, but he could also choose any one of a number of rate of change curves. In fact for pretension torque level A, curve 2 as shown in FIG. 8, (the hypothetically ideal curve) could be fairly closely approximated by choosing curve 6 of FIG. 9. Comparing the 18 tilt range S to T for curve 6, with the 18 tilt range S to T for curve 3, it will be seen that the slopes of the curves in these ranges are almost identical. Accordingly, the tilt rates for the chairs will be identical. If a person were to desire a higher pretension as is indicated by B in FIG. 9, he could similarly closely approximate curve 2 of FIG. 8 by choosing curve 7 of FIG. 9. Comparing the 18 tilt range for curve 7, X to 2 with the corresponding 18 range of operation for curve 2, X to Z, it will be seen that the slopes are almost identical.

The rotation of cam 70 to a particular position will not always give the same pretension force, since this factor is also dependent upon the position oflevers 51 and 54 and the other members of the adjustment assembly along the length of rods 21 and 41. For example, if levers 51 and 54 are located so as to give rods 21 and 41 curve 3, the rotation of cam 70 to impart to rods 21 and 41 T' of twist will result in a higher pretension than if T of twist were imparted to the rods 21 and 41 when located so as to give the rods 21 and 41 curve number 8.

Similarly, even though the location of levers 51 and 54 at a given point along rods 21 and 41 gives those rods an overall characteristic rate of change curve, the tilt rate obtained by tilting the chair through 18, will not necessarily be constant at a given location of levers 51 and 54 on torsion rods 21 and 41. Rotation of cam means 70 to various positions will result in difi'erent effective ranges of operation along the particular rate of change curve at that location of levers 51 and 54 along rods 21 and 41. For example if levers 51 and 54 are located to give the chair iron curve 7, you can still obtain different ranges of operation, for example X to Z rather than S to T, by rotating cam 70.

Consequently, while the particular pretension setting desired and the particular tilt rate desired can be chosen independently of each other, they are each determined by a combination of the location of assembly 50 along the length of rods 21 and 41 and by the rotational position of cam means 70. Thus, in essence, the adjustment assembly comprised of levers 51 and 54, channel 60 and cam 70 comprises a single assembly which achieves two separate functions.

in operation, both the circular discs 71 of cam means 70 and one of the torsion rods 21 or 41 might be graduated according to the weights of people who will be using the chair. Thus, there would be a pound setting for cam means 70 and a 140 pound setting along one ofthe torsion rods 21 or 41. By adjusting to both of these settings for 140 pounds, one would obtain the particular pretension and the particular rate of change curve which would be most desirable for a person weighing 140 pounds. In effect, one would be obtaining a desired pretension setting along curve number 2 of FIG. 8. Deviations from these normal settings could readily be made by any person who did not consider these normal values of pretension and rate of change curve to be desirable.

Thus, this invention provides a chair iron in which a persons choice of pretension does not limit his choice of tilt rate for the chair and vice versa. Difierent rates of change curves for the bias means, rods 21 and 41, can be selected. By using two torsion rods instead of one long one, the inventor provides a person with a greater variety of settings than could reasonably be provided with a single torsion rod. lf torsion rods 21 and 41 were placed end to end as a single torsion rod, the iron would be far too long and bulky to be attractive.

Furthermore, the use of two torsion rods 21 and 41 increases the variety of settings by increasing the range of degrees through which the torsion means 21 and 41 can be twisted. The twisting of each rod 21 and 41 through 5 is equivalent to twisting one long rod through 10.

Finally, the inventor has provided a chair iron which is not only small and attractive in appearance, but which is also readily and easily manufactured. Consequently, the tremendous advantages in comfort which are provided by this invention can be offered to the consumer at an extremely reasonable price.

It is understood that this is merely a preferred embodiment of the invention and that many changes and alterations can be made thereof without departing from the broader aspects and spirit of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A chair control comprising: a frame supportable by a base; a platform for supporting a seat, back or the like, pivotally mounted on said frame and being tiltable with respect to said frame; bias means for biasing said platform and said frame towards a normal position and for controlling the tilt rate of said control; said means having an initial bias which must be overcome in order to initiate tilting of said platform; means for varying said initial bias and said tilt rate independently of one another.

2. A chair control comprising: a frame supportable by a base; a platform for supporting a seat, back or the like, pivotally mounted on said frame and being tiltable with respect thereto; a torsion rod being operably connected to said frame and being fixed at one point against rotation with respect thereto; said torsion rod being operably connected to said platform at a distance from said operable connection to said frame whereby tilting of said platform imparts a twist to said torsion rod; means for varying the distance between said operable connection to said frame and said operable connection to said platform; means for imparting an initial twist to said torsion rod without tilting said platform.

3. The chair iron of claim 2 which includes: said frame having two ends; said torsion rod having two ends and being operably connected to said frame by being mounted between the ends of said frame; one end of said torsion rod being fixed against rotation and the other end being free to rotate; said torsion rod being operably connected to said platform through a lever being mounted at one end on said torsion bar but being fixed against rotation with respect thereto; the free end of said lever being operably connected to said platform such that tilting of said platform causes said lever to twist said torsion rod; said means for varying the distance between said operable connection of said torsion rod to said first frame and said operable connection of said torsion rod to said second frame comprising said lever being slidable along the length of said torsion rod whereby the effective length of said rod can be varied.

4. The chair iron of claim 3 in which said means for imparting an initial twist comprises means for varying the initial angle between said platform and said lever whereby the initial twist of said torsion rod can be varied without tilting said platform.

5. A chair iron comprising: a frame having first and second ends and being mounted on a base; a platform for supporting a seat, back or the like, having first and second ends, said first and second ends being pivotally connected to said first and second ends of said frame respectively such that said platform is tiltable with respect to said frame; a first torsion rod being mounted at its two ends on said frame, one end of said rod being free to rotate in said first end and the other end being fixed against rotation in said second end; a second torsion rod being mounted in said platform in the same fashion, parallel to said first torsion rod; a first lever being slidably mounted on said first torsion rod and being fixed against rotation with respect thereto; a second lever being slidably mounted on said second torsion rod and being fixed against rotation with respect thereto; said first and second levers extending inwardly towards each other; bracket means holding said first and second levers in juxtaposition and holding the ends of said levers in a fixed relationship.

6. The chair iron of claim 5 which also includes a means for imparting a force on said levers without tilting said platform whereby an initial twist can be imparted to said torsion rods.

7. The chair iron of claim 6 wherein said means for imparting force on said levers comprises: said bracket including a first fulcrum which engages said first lever and a second fulcrum which engages said second lever; said bracket including means for pivoting said levers on said fulcrums.

8. The chair iron of claim 7 wherein said means for pivoting said levers on said fulcrums includes a member movably mounted in said bracket and engaging the ends of said levers; means for moving said member with respect to said brackets whereby said levers pivot on said fulcrums.

9. The chair iron of claim 8 wherein said bracket means includes a base. said first and second fulcrums being located on one surface thereof; said moveably mounted member comprising a pin extending through said base and up between the ends of said levers; said pin including a cross piece at its top which extends over the ends of each of said lever; means for moving said member comprising means for moving said pin downwardly through said base or allowing it to be pulled upwardly by the action of said torsion rods twisting said levers upwardly.

10. The chair iron of claim 9 wherein said means for moving said pin comprises a cam member mounted on the surface of said base which is opposite of the surface on which said fulcrums are located; said pin including a hook extending over and engaging said cam member.

11. The chair iron of claim 10 wherein said cam member comprises a circular inclined ramp being rotatably mounted at its center on said base; said ramp including a handle whereby it can be rotated; said hook engaging said inclined ramp.

12. A chair iron comprising: a frame supportable by a base; a platform for supporting a chair seat, back or the like,

mounted on said frame and being tiltable with respect to said frame; a first torsion rod being operably connected to said frame and being fixed at one point against rotation with respect thereto; a second torsion rod being operably connected to said platform and being fixed at one point against rotation with respect thereto; a first lever being operably connected to said first torsion rod and being fixed against rotation with respect thereto; a second lever being operably connected to said second torsion rod and being fixed against rotation with respect thereto; said first and second levers extending inwardly towards each other; bracket means holding said first and second levers in juxtaposition and holding the ends of said levers in a fixed relationship; said bracket means including a first fulcrum which engages said first lever and a second fulcrum which engages said second lever; said bracket means including means for pivoting said levers on said fulcrums.

13. The chair iron of claim 12 wherein said means for pivoting said levers on said fulcrums includes a member movably mounted in said bracket and engaging the ends of said levers; means for moving said member with respect to said brackets whereby said levers pivot on said fulcrums.

14. The chair iron of claim 13 wherein said bracket means includes a base, said first and second fulcrums being located on one surface thereof; said movably mounted member comprising a pin extending through said base and up between the ends of said levers; said pin including a cross piece at its top which extends over the ends of each of said lever; means for moving said member comprising means for moving said pin downwardly through said base or allowing it to be pulled upwardly by the action of said torsion rods twisting said levers upwardly.

15. The chair iron of claim 14 wherein said means for moving said pin comprises a cam member mounted on the surface of said base which is opposite of the surface on which said fulcrums are located; said pin including a hook extending over and engaging said cam member.

16. The chair iron of claim 15 wherein said cam member comprises a circular inclined ramp being rotatably mounted at its center on said base; said ramp including a handle whereby it can be rotated; said hook engaging said inclined ramp.

17. In a chair control having a frame for mounting on a base and a platform for supporting a chair seat, back or the like, tiltably mounted on said frame, the improvement comprising: a first torsion bar operably connected to said frame with one end fixed against rotation with respect to said frame and with its other end free to rotate; a second torsion bar operably connected to said platform with one end fixed against rotation with respect to said platform and with its other end free to rotate; a first lever operably connected to said first torsion bar and being fixed against rotation with respect thereto; a second lever operably connected to said second torsion bar and being fixed against rotation with respect thereto; said first and second levers extending inwardly towards one another; bracket means holding the ends of said first and second levers in juxtaposition.

18. The chair control of claim 17 which also includes a means for imparting a force on said levers without tilting said platform whereby an initial twist can be imparted to said torsion rods.

19. The chair control of claim 18 wherein said means for imparting force on said levers comprises: said bracket including a first fulcrum which engages said first lever and a second fulcrum which engages said second lever; said bracket including means for pivoting said levers on said fulcrums.

20. The chair control of claim 19 wherein said means for pivoting said levers on said fulcrums includes a member movably mounted in said bracket and engaging the ends of said levers; means for moving said member with respect to said brackets whereby said levers pivot on said fulcrums.

21. The chair control of claim 20 wherein said bracket means includes a base, said first and second fulcrums being located on one surface thereof; said movably mounted member comprising a pin extending through said base and up between the ends of said levers; said pin including a cross piece at its top which extends over the ends of each of said lever; means for moving said member comprising means for moving said pin downwardly through said base or allowing it to be pulled upwardly by the action of said torsion bars twisting said levers upwardly.

22. The chair control of claim 21 wherein said means for moving said pin comprises a cam member mounted on the surface of said base which is opposite of the surface on which said fulcrums are located; said pin including a hook extending over and engaging said cam member.

23. The chair control of claim 22 wherein said cam member comprises a circular inclined ramp being rotatably mounted at its center on said base; said ramp including a handle whereby it can be rotated; said hook engaging said inclined ramp.

24. In a chair control having a frame for mounting on a base and a platform for supporting a chair seat, back or the like, tiltably mounted on said frame, the improvement comprising: a first torsion bar operably connected to said frame with one end fixed against rotation with respect to said frame and with its other end free to rotate; a second torsion bar operably connected to said platform with one end fixed against rotation with respect to said platform and with its other end free to rotate; means interconnecting said first and second torsion bars whereby rotation in one generates rotation in the other; means for imparting a pretensioning twist to said torsion bars without tilting said platform.

25. The chair control of claim 24 in which said means interconnecting said first and second torsion bars comprises: a first lever operably connected to said first torsion bar and being fixed against rotation with respect thereto; a second lever operably connected to said second torsion bar and being fixed against rotation with respect thereto; said first and second levers extending inwardly towards one another; bracket means holding the ends of said first and second levers in juxtaposition.

26. The chair control of claim 25 in which said pretension ing means includes a means for imparting a force on said levers without tilting said platform whereby an initial twist can be imparted to said torsion rods.

27. The chair control of claim 26 in which: said fixed end of said first torsion bar is mounted in a first side of said frame; said fixed end of said second torsion bar is mounted in a first side of said platform; said first side of said platform being pivotally connected to said first side of said frame; said interconnecting means interconnecting said first and second torsion bars at a point spaced from said fixed ends of said bars.

28. The chair control of claim 29 in which said other end of said first torsion bar is rotatably mounted in the second side of said frame and in which the other end of said second torsion bar is rotatably mounted in the second side of said platform, said second side of said platform being pivotally connected to said second side of said frame.

29. In a chair control having a frame for mounting on a base and a platform for supporting a chair seat, back or the like, tiltably mounted on said frame, the improvement comprising: a generally U-shaped torsion means for generating a returning force when said platform is tilted with respect to said frame; said torsion means including a first bar-like leg and a second bar-like leg joined by an interconnecting base; the free end of said first leg being operably connected to said frame and being fixed against rotation with respect thereto; and the free end of said second leg being operably connected to said platform and being fixed against rotation with respect thereto; said interconnecting base including a first lever extending inwardly from said first leg, a second lever extending inwardly from said second leg and means joining said levers such that the angle of orientation of one of said levers with respect to the other can be varied while movement of one of said levers generates movement of the other.

30. The chair control of claim 29 in which said joining means comprises a bracket having a first fulcrum which engages said first lever, a second fulcrum which engages said second lever and a member engaging the ends of said levers, holding said levers against said fulcrums.

31. In a chair control having a frame for mounting on a base and a platform for supporting a chair seat, back or the like, tiltably mounted on said frame, the improvement comprising: a first torsion means operably connected to said frame and being fixed at one point against rotation with respect to said frame and having a second point free to rotate; a second torsion means operably connected to said platform and being fixed at one point against rotation with respect to said platform and having a second point free to rotate; a first lever operably connected to said first torsion means at said second point and being fixed against rotation with respect thereto; a second lever operably connected to said second torsion means at said second point and being fixed against rotation with respect thereto; said first and second levers extending inwardly towards one another; bracket means holding the ends of said first and second levers in juxtaposition.

32. The chair control of claim 31 comprising: said bracket including a first fulcrum which engages said first lever and a second fulcrum which engages said second lever; said bracket including means for pivoting said levers on said fulcrums to pretension said torsion means.

33. The chair control of claim 32 wherein said means for pivoting said levers on said fulcrums includes a member movably mounted in said bracket and engaging the ends of said levers; means for moving said member with respect to said brackets whereby said levers pivot on said fulcrums.

34. The chair control of claim 33 wherein said bracket means includes a base, said first and second fulcrums being located on one surface thereof; said movably mounted member comprising a pin extending through said base and up between the ends of said levers; said pin including a cross piece at its top which extends over the ends of each of said lever; means for moving said member comprising means for moving said pin downwardly through said base or allowing it to be pulled upwardly by the action of said torsion bars twisting said levers upwardly.

35. A chair control comprising: a frame supportable by a base; a platfonn for supporting a seat, back or the like, mounted on said frame and being tiltable with respect to said frame; a torsion bar operably connected to said frame and being fixed at one point against rotation with respect thereto; lever means operably connected to said torsion bar and being fixed against rotation with respect thereto; said lever means being operably connected to said platform whereby tilting of said platform causes said lever to twist said torsion rod; said lever means being slidable along the length of said torsion bar; means for imparting an initial twist to said lever means without tilting said platform.

36. A chair control comprising: a frame supportable by a base; a platform for supporting a seat, back or the like, pivotally mounted on said frame and being tiltable with respect to said frame; torsion means operating between said frame and said platform, said torsion means being twisted through a length by tilting of said platform; an adjustment assembly operably connected to said torsion means and including first means for varying said length through which twist is imparted by the tilting of said platform and including second means acting independently of said first means for imparting an initial twist to said torsion means without tilting said platfonn.

37. The chair iron of claim 36 in which said torsion means comprises a first torsion rod mounted in said frame and being fixed at one point against rotation with respect thereto; said torsion means comprising a second torsion rod mounted on said platform, being parallel to said first rod and being fixed against rotation with respect to said platform at one point; said adjustment assembly comprising a first lever being slidably mounted on said first rod and being fixed against rotation with respect thereto and being operably connected at its free end to said platform; said adjustment assembly comprising a second lever being slidably mounted on said second rod and being levers and holding them in juxtaposition; said bracket means including a first fulcrum engaging said first lever and a second fulcrum engaging said second lever; said pretension means comprising means mounted on said bracket means for pivoting said first lever on said first fulcrum and for pivoting said second lever on said second fulcrum. 

1. A chair control comprising: a frame supportable by a base; a platform for supporting a seat, back or the like, pivotally mounted on said frame and being tiltable with respect to said frame; bias means for biasing said platform and said frame towards a normal position and for controlling the tilt rate of said control; said means having an initial bias which must be overcome in order to initiate tilting of said platform; means for varying said initial bias and said tilt rate independently of one another.
 2. A chair control comprising: a frame supportable by a base; a platform for supporting a seat, back or the like, pivotally mounted on said frame and being tiltable with respect thereto; a torsion rod being operably connected to said frame and being fixed at one point against rotation with respect thereto; said torsion rod being operably connected to said platform at a distance from said operable connection to said frame whereby tilting of said platform imparts a twist to said torsion rod; means for varying the distance between said operable connection to said frame and said operable connection to said platform; means for imparting an initial twist to said torsion rod without tilting said platform.
 3. The chair iron of claim 2 which includes: said frame having two ends; said torsion rod having two ends and being operably connected to said frame by being mounted between the ends of said frame; one end of said torsion rod being fixed against rotation and the other end being free to rotate; said torsion rod being operably connected to said platform through a lever being mounted at one end on said torsion bar but being fixed against rotation with respect thereto; the free end of said lever being operably connected to said platform such that tilting of said platform causes said lever to twist said torsion rod; said means for varying the distance between said operable connection of said torsion rod to said first frame and said operable connection of said torsion rod to said second frame comprising said lever being slidable along the length of said torsion rod whereby the effective length of said rod can be varied.
 4. The chair iron of claim 3 in which said means for imparting an initial twist comprises means for varying the initial angle between said platform and said lever whereby the initial twist of said torsion rod can be varied without tilting said platform.
 5. A chair iron comprising: a frame having first and second ends and being mounted on a base; a platform for supporting a seat, back or the like, having first and second ends, saId first and second ends being pivotally connected to said first and second ends of said frame respectively such that said platform is tiltable with respect to said frame; a first torsion rod being mounted at its two ends on said frame, one end of said rod being free to rotate in said first end and the other end being fixed against rotation in said second end; a second torsion rod being mounted in said platform in the same fashion, parallel to said first torsion rod; a first lever being slidably mounted on said first torsion rod and being fixed against rotation with respect thereto; a second lever being slidably mounted on said second torsion rod and being fixed against rotation with respect thereto; said first and second levers extending inwardly towards each other; bracket means holding said first and second levers in juxtaposition and holding the ends of said levers in a fixed relationship.
 6. The chair iron of claim 5 which also includes a means for imparting a force on said levers without tilting said platform whereby an initial twist can be imparted to said torsion rods.
 7. The chair iron of claim 6 wherein said means for imparting force on said levers comprises: said bracket including a first fulcrum which engages said first lever and a second fulcrum which engages said second lever; said bracket including means for pivoting said levers on said fulcrums.
 8. The chair iron of claim 7 wherein said means for pivoting said levers on said fulcrums includes a member movably mounted in said bracket and engaging the ends of said levers; means for moving said member with respect to said brackets whereby said levers pivot on said fulcrums.
 9. The chair iron of claim 8 wherein said bracket means includes a base, said first and second fulcrums being located on one surface thereof; said moveably mounted member comprising a pin extending through said base and up between the ends of said levers; said pin including a cross piece at its top which extends over the ends of each of said lever; means for moving said member comprising means for moving said pin downwardly through said base or allowing it to be pulled upwardly by the action of said torsion rods twisting said levers upwardly.
 10. The chair iron of claim 9 wherein said means for moving said pin comprises a cam member mounted on the surface of said base which is opposite of the surface on which said fulcrums are located; said pin including a hook extending over and engaging said cam member.
 11. The chair iron of claim 10 wherein said cam member comprises a circular inclined ramp being rotatably mounted at its center on said base; said ramp including a handle whereby it can be rotated; said hook engaging said inclined ramp.
 12. A chair iron comprising: a frame supportable by a base; a platform for supporting a chair seat, back or the like, mounted on said frame and being tiltable with respect to said frame; a first torsion rod being operably connected to said frame and being fixed at one point against rotation with respect thereto; a second torsion rod being operably connected to said platform and being fixed at one point against rotation with respect thereto; a first lever being operably connected to said first torsion rod and being fixed against rotation with respect thereto; a second lever being operably connected to said second torsion rod and being fixed against rotation with respect thereto; said first and second levers extending inwardly towards each other; bracket means holding said first and second levers in juxtaposition and holding the ends of said levers in a fixed relationship; said bracket means including a first fulcrum which engages said first lever and a second fulcrum which engages said second lever; said bracket means including means for pivoting said levers on said fulcrums.
 13. The chair iron of claim 12 wherein said means for pivoting said levers on said fulcrums includes a member movably mounted in said bracket and engaging the ends of said levers; means for movIng said member with respect to said brackets whereby said levers pivot on said fulcrums.
 14. The chair iron of claim 13 wherein said bracket means includes a base, said first and second fulcrums being located on one surface thereof; said movably mounted member comprising a pin extending through said base and up between the ends of said levers; said pin including a cross piece at its top which extends over the ends of each of said lever; means for moving said member comprising means for moving said pin downwardly through said base or allowing it to be pulled upwardly by the action of said torsion rods twisting said levers upwardly.
 15. The chair iron of claim 14 wherein said means for moving said pin comprises a cam member mounted on the surface of said base which is opposite of the surface on which said fulcrums are located; said pin including a hook extending over and engaging said cam member.
 16. The chair iron of claim 15 wherein said cam member comprises a circular inclined ramp being rotatably mounted at its center on said base; said ramp including a handle whereby it can be rotated; said hook engaging said inclined ramp.
 17. In a chair control having a frame for mounting on a base and a platform for supporting a chair seat, back or the like, tiltably mounted on said frame, the improvement comprising: a first torsion bar operably connected to said frame with one end fixed against rotation with respect to said frame and with its other end free to rotate; a second torsion bar operably connected to said platform with one end fixed against rotation with respect to said platform and with its other end free to rotate; a first lever operably connected to said first torsion bar and being fixed against rotation with respect thereto; a second lever operably connected to said second torsion bar and being fixed against rotation with respect thereto; said first and second levers extending inwardly towards one another; bracket means holding the ends of said first and second levers in juxtaposition.
 18. The chair control of claim 17 which also includes a means for imparting a force on said levers without tilting said platform whereby an initial twist can be imparted to said torsion rods.
 19. The chair control of claim 18 wherein said means for imparting force on said levers comprises: said bracket including a first fulcrum which engages said first lever and a second fulcrum which engages said second lever; said bracket including means for pivoting said levers on said fulcrums.
 20. The chair control of claim 19 wherein said means for pivoting said levers on said fulcrums includes a member movably mounted in said bracket and engaging the ends of said levers; means for moving said member with respect to said brackets whereby said levers pivot on said fulcrums.
 21. The chair control of claim 20 wherein said bracket means includes a base, said first and second fulcrums being located on one surface thereof; said movably mounted member comprising a pin extending through said base and up between the ends of said levers; said pin including a cross piece at its top which extends over the ends of each of said lever; means for moving said member comprising means for moving said pin downwardly through said base or allowing it to be pulled upwardly by the action of said torsion bars twisting said levers upwardly.
 22. The chair control of claim 21 wherein said means for moving said pin comprises a cam member mounted on the surface of said base which is opposite of the surface on which said fulcrums are located; said pin including a hook extending over and engaging said cam member.
 23. The chair control of claim 22 wherein said cam member comprises a circular inclined ramp being rotatably mounted at its center on said base; said ramp including a handle whereby it can be rotated; said hook engaging said inclined ramp.
 24. In a chair control having a frame for mounting on a base and a platform for supporting a chair seat, back or the like, tiltably mounted on saId frame, the improvement comprising: a first torsion bar operably connected to said frame with one end fixed against rotation with respect to said frame and with its other end free to rotate; a second torsion bar operably connected to said platform with one end fixed against rotation with respect to said platform and with its other end free to rotate; means interconnecting said first and second torsion bars whereby rotation in one generates rotation in the other; means for imparting a pretensioning twist to said torsion bars without tilting said platform.
 25. The chair control of claim 24 in which said means interconnecting said first and second torsion bars comprises: a first lever operably connected to said first torsion bar and being fixed against rotation with respect thereto; a second lever operably connected to said second torsion bar and being fixed against rotation with respect thereto; said first and second levers extending inwardly towards one another; bracket means holding the ends of said first and second levers in juxtaposition.
 26. The chair control of claim 25 in which said pretensioning means includes a means for imparting a force on said levers without tilting said platform whereby an initial twist can be imparted to said torsion rods.
 27. The chair control of claim 26 in which: said fixed end of said first torsion bar is mounted in a first side of said frame; said fixed end of said second torsion bar is mounted in a first side of said platform; said first side of said platform being pivotally connected to said first side of said frame; said interconnecting means interconnecting said first and second torsion bars at a point spaced from said fixed ends of said bars.
 28. The chair control of claim 29 in which said other end of said first torsion bar is rotatably mounted in the second side of said frame and in which the other end of said second torsion bar is rotatably mounted in the second side of said platform, said second side of said platform being pivotally connected to said second side of said frame.
 29. In a chair control having a frame for mounting on a base and a platform for supporting a chair seat, back or the like, tiltably mounted on said frame, the improvement comprising: a generally U-shaped torsion means for generating a returning force when said platform is tilted with respect to said frame; said torsion means including a first bar-like leg and a second bar-like leg joined by an interconnecting base; the free end of said first leg being operably connected to said frame and being fixed against rotation with respect thereto; and the free end of said second leg being operably connected to said platform and being fixed against rotation with respect thereto; said interconnecting base including a first lever extending inwardly from said first leg, a second lever extending inwardly from said second leg and means joining said levers such that the angle of orientation of one of said levers with respect to the other can be varied while movement of one of said levers generates movement of the other.
 30. The chair control of claim 29 in which said joining means comprises a bracket having a first fulcrum which engages said first lever, a second fulcrum which engages said second lever and a member engaging the ends of said levers, holding said levers against said fulcrums.
 31. In a chair control having a frame for mounting on a base and a platform for supporting a chair seat, back or the like, tiltably mounted on said frame, the improvement comprising: a first torsion means operably connected to said frame and being fixed at one point against rotation with respect to said frame and having a second point free to rotate; a second torsion means operably connected to said platform and being fixed at one point against rotation with respect to said platform and having a second point free to rotate; a first lever operably connected to said first torsion means at said second point and being fixed against rotation with respect thereto; a seconD lever operably connected to said second torsion means at said second point and being fixed against rotation with respect thereto; said first and second levers extending inwardly towards one another; bracket means holding the ends of said first and second levers in juxtaposition.
 32. The chair control of claim 31 comprising: said bracket including a first fulcrum which engages said first lever and a second fulcrum which engages said second lever; said bracket including means for pivoting said levers on said fulcrums to pretension said torsion means.
 33. The chair control of claim 32 wherein said means for pivoting said levers on said fulcrums includes a member movably mounted in said bracket and engaging the ends of said levers; means for moving said member with respect to said brackets whereby said levers pivot on said fulcrums.
 34. The chair control of claim 33 wherein said bracket means includes a base, said first and second fulcrums being located on one surface thereof; said movably mounted member comprising a pin extending through said base and up between the ends of said levers; said pin including a cross piece at its top which extends over the ends of each of said lever; means for moving said member comprising means for moving said pin downwardly through said base or allowing it to be pulled upwardly by the action of said torsion bars twisting said levers upwardly.
 35. A chair control comprising: a frame supportable by a base; a platform for supporting a seat, back or the like, mounted on said frame and being tiltable with respect to said frame; a torsion bar operably connected to said frame and being fixed at one point against rotation with respect thereto; lever means operably connected to said torsion bar and being fixed against rotation with respect thereto; said lever means being operably connected to said platform whereby tilting of said platform causes said lever to twist said torsion rod; said lever means being slidable along the length of said torsion bar; means for imparting an initial twist to said lever means without tilting said platform.
 36. A chair control comprising: a frame supportable by a base; a platform for supporting a seat, back or the like, pivotally mounted on said frame and being tiltable with respect to said frame; torsion means operating between said frame and said platform, said torsion means being twisted through a length by tilting of said platform; an adjustment assembly operably connected to said torsion means and including first means for varying said length through which twist is imparted by the tilting of said platform and including second means acting independently of said first means for imparting an initial twist to said torsion means without tilting said platform.
 37. The chair iron of claim 36 in which said torsion means comprises a first torsion rod mounted in said frame and being fixed at one point against rotation with respect thereto; said torsion means comprising a second torsion rod mounted on said platform, being parallel to said first rod and being fixed against rotation with respect to said platform at one point; said adjustment assembly comprising a first lever being slidably mounted on said first rod and being fixed against rotation with respect thereto and being operably connected at its free end to said platform; said adjustment assembly comprising a second lever being slidably mounted on said second rod and being fixed against rotation with respect thereto and being operably connected at its free end to said frame: said adjustment assembly comprising means for imparting a force on said free ends of said slidable levers whereby said torsion rods receive an initial twist without the tilting of said platform.
 38. The chair iron of claim 37 wherein said adjustment assembly also includes said first and second levers extending inwardly towards one another; bracket means embracing said levers and holding them in juxtaposition; said bracket means including a first fulcrum engaging said first lever and a secOnd fulcrum engaging said second lever; said pretension means comprising means mounted on said bracket means for pivoting said first lever on said first fulcrum and for pivoting said second lever on said second fulcrum. 